A research effort spearheaded by the University of Arizona has employed dendrochronology, the study of tree rings, to ascertain that significant seismic activities took place in the Puget Lowlands of western Washington approximately a millennium ago due to a network of shallow faults. This information holds implications for the modern residents of the area, and indicates that existing seismic hazard models may require reevaluation.
This revelation could influence future earthquake preparedness strategies for the region.
Earlier this year, a seismic event measuring 7.8 on the Richter scale occurred along the Turkey-Syria border, followed by another almost equally powerful quake nine hours later. Shallow faults located less than 18 miles below the Earth’s surface were implicated in causing these catastrophic events, resulting in the collapse of thousands of buildings and the loss of tens of thousands of lives.
Parallels can be drawn to shallow faults in the Puget Lowlands, which research shows were active about 1,000 years ago. Tree-ring data indicates that these seismic disturbances happened either in the latter part of A.D. 923 or the early months of A.D. 924. The study’s findings have serious implications for the region, currently home to over 4 million people, including the cities of Seattle, Tacoma, and Olympia. The research has been published in the journal Science Advances.
Table of Contents
Characteristics of Historical Seismic Events
The researchers found that the ancient seismic event was caused either by the simultaneous rupture of all shallow faults in the region, resulting in an earthquake with an estimated magnitude of 7.8, or by twin earthquakes occurring in close succession with magnitudes estimated at 7.5 and 7.3. Typically, shallow faults are responsible for more intense and localized seismic activity compared to other geological formations.
Interconnected Fault Systems
The study identifies a novel interconnectedness among these shallow faults, either through underground linkages or via stress transfer between faults. Current regional hazard models for engineering design and policy development do not incorporate this newfound information, according to Bryan Black, the study’s lead author and an associate professor of dendrochronology at the University of Arizona.
Focused Research on Shallow Faults
Researchers have been identifying shallow faults in this region since the 1960s. The initial discovery was the Seattle Fault, later followed by the Saddle Mountain, Tacoma, and Olympia faults. These faults had previously been identified as being active around 1,000 years ago during a series of earthquakes known as the “millennial cluster.”
Role of Dendrochronology in Seismic Research
Tree rings offer unique insights into the history of climatic and environmental conditions. These natural markers can help scientists determine the exact years when trees lived and died. For this study, samples were taken from trees that perished due to ancient seismic activities. By comparing these with living trees, researchers were able to pinpoint the years of seismic events.
Confirming the Data
In addition, the study employed radiocarbon measurements correlated with a significant solar storm occurring between 774 and 775 A.D., offering another method to validate their findings.
Significance and Future Implications
The research conclusively indicates that seismic activities across various faults in the region are interconnected. Bryan Black stated that the current models should be updated to reflect the possibility of these faults rupturing either synchronously or in quick succession.
He also warned that if such an event were to occur today, the impact could be as devastating as the 1906 earthquake in San Francisco, with significant damage to infrastructure and a likelihood of triggering landslides and local tsunamis. While such catastrophic events are infrequent, their potential for immense damage should not be underestimated.
Reference: “A multifault earthquake threat for the Seattle metropolitan region revealed by mass tree mortality” by Bryan A. Black et al., published on September 27, 2023, in Science Advances. DOI: 10.1126/sciadv.adh4973
Frequently Asked Questions (FAQs) about seismic threat in the Puget Lowlands
What is the main focus of the research led by the University of Arizona?
The research primarily aims to understand the seismic activity in the Puget Lowlands of western Washington through the study of tree rings, also known as dendrochronology. The study uncovers that significant earthquakes occurred approximately 1,000 years ago due to a network of shallow faults in the region.
What methodology was used to conduct this research?
The study employed dendrochronology, which involves analyzing tree rings to understand historical and environmental conditions. Researchers collected samples from both living and dead trees to pinpoint the years when significant seismic events occurred.
How could these findings affect current hazard models?
The study suggests that current hazard models may need to be revised to incorporate the interconnected nature of shallow faults in the Puget Lowlands. These models are used for engineering design and policymaking related to seismic preparedness.
What are the implications for residents in the affected area?
The findings indicate a potential risk for over 4 million people residing in western Washington, including the cities of Seattle, Tacoma, and Olympia. The study posits that a repeat seismic event could have devastating consequences.
How does the study relate to other seismic events around the world?
The study draws parallels to a recent 7.8-magnitude earthquake along the Turkey-Syria border, which was also caused by shallow faults. It implies that similar geological configurations can result in intense and focused seismic activities.
What is the “millennial cluster” mentioned in the study?
The “millennial cluster” refers to a series of earthquakes that occurred around 1,000 years ago in the Puget Lowlands, as evidenced by dendrochronological data. The faults involved include the Seattle Fault, the Saddle Mountain Fault, and others.
Was radiocarbon dating used in the research?
Yes, radiocarbon dating was employed to corroborate the dendrochronological findings. A significant solar storm between 774 and 775 A.D. caused a global spike in radiocarbon, which was used as a reference point to validate the dates of the earthquake-killed trees.
What publication released the findings of this study?
The research findings were published in the journal Science Advances, under the title “A multifault earthquake threat for the Seattle metropolitan region revealed by mass tree mortality.”
How was the exact timing of the ancient seismic events determined?
By comparing the growth patterns in tree rings from dead trees affected by the seismic events with those from living trees, the researchers were able to narrow down the timing to either late A.D. 923 or early A.D. 924.
What could be the potential scale of damage if such an earthquake occurs again?
According to the study’s lead author, Bryan Black, a similar earthquake today could be as catastrophic as the 1906 earthquake in San Francisco. This could result in severe damage to infrastructure, landslides, and local tsunamis.
More about seismic threat in the Puget Lowlands
- University of Arizona Laboratory for Tree-Ring Research
- Science Advances Journal
- Seismic Hazard Models
- Dendrochronology Explained
- The 1906 San Francisco Earthquake
- Understanding Shallow Faults
- Radiocarbon Dating
- Puget Sound Seismic Network
- Earthquake Preparedness Guidelines
9 comments
Research like this is critical for city planning and disaster preparedness. Think its high time to revise those hazard models and make policy changes.
Been living in Tacoma for years and honestly this is a wake up call. Time to reevaluate the earthquake kit, maybe add a few more canned goods.
Its fascinating how science has all these ways to look back in time. Tree rings, who would’ve thought? Looks like our ancestors had quite a shake, hope we’re more prepared now.
Radiocarbon dating and tree rings, science at its best. Gives a whole new perspective on how interconnected our world really is.
As an environmental science student, this kinda research makes me really excited. Shallow faults huh? Definitely something to dig deeper into. Literally.
Late A.D. 923 or early 924, thats some precise dating. Curious about how much more we can learn about our past using such methods.
This is kinda scary. Got family in Seattle and the thought of a big earthquake there is just terrifying. Glad they’re doing the research but what’s being done about it?
Dendrochronology’s the word of the day, folks. Who knew trees could tell us so much, and not just about climate but seismic activity too.
Wow, this is pretty eye-opening. Always knew the Pacific Northwest was earthquake-prone, but tree rings revealing past quakes? thats next level.